Occasionally YAPI wont start after upgrade showing “System.MissingMethodException: Method not found” error message. The cause of this problem is an interrupted upgrade process when some modules were not updated properly.
To avoid this problem let YAPI Upgrade process to finish. Do not start YAPI after upgrade – YAPI will restart automatically after update completes. Typically, the upgrade process takes just a few seconds but occasionally may take a minute or two.
Unfortunately, once in a while we are getting support calls reporting this exact problem Here is a quick fix: download YAPIUpdateFix.exe app using this link http://yapi.me/downloads/YAPIUpdateFix.exe Run app on a computer that reported YAPI problem, follow instructions.